The present disclosure relates to a developing device incorporated in an image forming apparatus exploiting electrophotography, such as a copier, a printer, a facsimile machine, or a multifunction peripheral thereof, and to an image forming apparatus incorporating the developing device. More particularly, the present disclosure relates to a developing device which can be replenished with new two-component developer containing toner and carrier and meanwhile discharge surplus developer, and to an image forming apparatus incorporating such a developing device.
In an image forming apparatus, an electrostatic latent image formed on an image carrying member comprising a photosensitive member or the like is made visible by being developed into a toner image by a developing device. Some such developing devices adopt a two-component developing system that uses two-component developer. In this type of developing device, two-component developer containing carrier and toner is stored in a developer container, a developing roller is arranged for feeding the developer to the image carrying member, and a stirring member is arranged for feeding, while stirring and transporting, the developer in the developer container to the developing roller.
In a developing device adopting a two-component developing system, toner is consumed in developing operation, whereas carrier is left unconsumed in the developing device. Thus, carrier stirred together with toner inside the developer container deteriorates under mechanical stress as the carrier is stirred repeatedly, gradually diminishing the toner charging performance of the carrier.
As a solution, developing devices have been proposed that supply fresh developer containing carrier and toner into a developer container while discharging surplus developer so as to suppress degradation in charging performance.
For example, a developing device is known that includes a transport screw (first transporting portion) for transporting developer, a return screw (second transporting portion) arranged on the downstream side of the transport screw with respect to the transport direction of the transport screw, and a discharge screw (third transporting portion) arranged on the upstream side of the return screw with respect to the transport direction of the return screw for transporting the developer toward a discharge port, wherein a disk is provided between the return screw (second transporting portion) and the discharge screw (third transporting portion). The disk serves as a circular wall to push back a large part of the developer moving toward the discharge port so that no excessive developer is discharged through the discharge port.